2.8 μm all-fiber laser based on dual-wavelength co-pumped cladding

Abstract

This application provides a 2.8μm all-fiber laser based on dual-wavelength synergistic cladding pumping. The laser includes a first pump source, a mid-infrared pump combiner, a high-reflectivity fiber grating, a first cladding gain fiber, a low-reflectivity fiber grating, a first mode stripper, and an end cap. The first pump source includes at least one first pump source providing a first wavelength and at least one second pump source providing a second wavelength. The mid-infrared pump combiner combines the first and second pump lights and couples them to the first cladding gain fiber. The high-reflectivity fiber grating and the low-reflectivity fiber grating form a resonant cavity. The first mode stripper strips the cladding light. The end cap outputs the laser and protects the end face. By employing dual-wavelength pump source synergistic excitation and an integrated all-fiber structure, this laser has advantages such as high energy conversion efficiency, compact and stable structure, and optimized pump light utilization efficiency.

Description

TECHNICAL FIELD

[0001] The present specification relates to the technical field of laser, in particular to a 2.8 μm all-fiber laser based on dual-wavelength cooperative cladding pumping. BACKGROUND

[0002] 2.8 μm band laser can realize precise tissue cutting and coagulation in medical surgery, is suitable for high-sensitivity gas component analysis in environmental monitoring, can complete fine material processing in industrial processing, and is used for remote target detection in national defense security field. Therefore, realizing high power, high efficiency and all-fiber output of the laser in this band becomes the core goal of current technical development. However, the existing technical solutions face multiple bottlenecks in actual application: the traditional single-wavelength pumping method cannot fully excite the gain medium, resulting in limited energy conversion efficiency; in order to improve the output power, it is often necessary to rely on free-space optical elements, which not only introduces additional loss, but also destroys the stability and compactness of the all-fiber structure; at the same time, the application of cladding pumping technology in the 2.8 μm band is restricted by the absorption characteristics of the gain fiber material, and it is difficult to effectively coordinate the pumping light utilization efficiency and the high-power output demand. These defects make it difficult for the existing solutions to achieve synergistic optimization in the three key dimensions of high efficiency, high power and all-fiber, which seriously restricts the promotion and application of 2.8 μm laser in actual scenarios. SUMMARY

[0003] The purpose of the present application is to provide a 2.8 μm all-fiber laser based on dual-wavelength cooperative cladding pumping, which has the advantages of improving energy conversion efficiency, ensuring the stability and compactness of the all-fiber structure, and optimizing the utilization efficiency of pumping light.

[0004] The present application provides a 2.8 μm all-fiber laser based on dual-wavelength cooperative cladding pumping, which comprises:

[0005] The first pump source comprises at least one first pump light source and at least one second pump light source, the first pump light source is configured to provide first pump light with a first wavelength, and the second pump light source is configured to provide second pump light with a second wavelength;

[0006] The first cladding gain fiber is configured to absorb the first pump light and the second pump light and amplify the generated laser to form a 2.8 μm laser;

[0007] The mid-infrared pump combiner is connected between the first pump source and the first cladding gain fiber, and is configured to couple the first pump light and the second pump light into the first cladding gain fiber;

[0008] a high-reflectivity fiber grating connected between an output end of the mid-infrared pump combiner and an input end of the first cladding-pumped gain fiber;

[0009] a low-reflectivity fiber grating connected to an output end of the first cladding-pumped gain fiber;

[0010] a first mode stripper connected to an output end of the low-reflectivity fiber grating;

[0011] an end cap connected to an output end of the first mode stripper.

[0012] In some embodiments of the present application, the first wavelength is 976 nm and the second wavelength is 1.7 μm.

[0013] In some embodiments of the present application, the first wavelength and the second wavelength are both 1.7 μm.

[0014] In some embodiments of the present application, the first cladding-pumped gain fiber is a fluoride-doped cladding-pumped gain fiber.

[0015] In some embodiments of the present application, further comprising a mid-infrared isolator connected between the first mode stripper and the end cap;

[0016] a second pump source comprising at least one third pump source configured to provide third pump light having a third wavelength and at least one fourth pump source configured to provide fourth pump light having a fourth wavelength;

[0017] a pump signal combiner connected to the mid-infrared isolator and the second pump source, respectively, the pump signal combiner being configured to couple the 2.8 μm laser light, the third pump light and the fourth pump light into a second cladding-pumped gain fiber;

[0018] the second cladding-pumped gain fiber connected to an output end of the pump signal combiner, the second cladding-pumped gain fiber being configured to absorb the 2.8 μm laser light, the third pump light and the fourth pump light and to amplify the resulting laser light;

[0019] a second mode stripper connected between the second cladding-pumped gain fiber and the end cap.

[0020] In some embodiments of the present application, the third wavelength is 976 nm and the fourth wavelength is 1.7 μm.

[0021] In some embodiments of the present application, the third wavelength and the fourth wavelength are both 1.7 μm.

[0022] In some embodiments of the present application, the second cladding-pumped gain fiber is a fluoride-doped cladding-pumped gain fiber.

[0023] In some embodiments of the present application, the ports of the pump signal combiner are fluoride fibers.

[0024] In some embodiments of the present application, a water-cooled plate is further included for dissipating heat from the all-fiber laser.

[0025] As can be seen from the above, the 2.8 μm all-fiber laser based on dual-wavelength collaborative cladding pumping provided by the embodiments of the present application includes a first pumping source, a first cladding gain fiber, a mid-infrared pump combiner, a high-reflection fiber grating, a low-reflection fiber grating, a first mode stripper, and an end cap. The dual-wavelength pumping sources work collaboratively and utilize the all-fiber assembly to efficiently generate and amplify 2.8 μm laser. The problems of low efficiency, unstable structure, and insufficient utilization of pump in the conventional scheme are solved. The 2.8 μm all-fiber laser based on dual-wavelength collaborative cladding pumping has the advantages of improving energy conversion efficiency, ensuring stability and compactness of the all-fiber structure, and optimizing utilization efficiency of pump light. BRIEF DESCRIPTION OF DRAWINGS

[0026] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The detailed description is made with reference to the accompanying drawings.

[0027] Figure 1 The structural block schematic diagram of the 2.8 μm all-fiber laser based on dual-wavelength collaborative cladding pumping provided by some embodiments of the present application is shown.

[0028] Figure 2 The structural block schematic diagram of the 2.8 μm all-fiber laser based on dual-wavelength collaborative cladding pumping provided by some embodiments of the present application is shown.

[0029] Figure 3 The erbium ion transition energy level diagram.

[0030] 10-2.8 μm all-fiber laser based on dual-wavelength collaborative cladding pumping;

[0031] 100-first pumping source, 100a-first pumping light source, 100b-second pumping light source;

[0032] 200-mid-infrared pump combiner;

[0033] 300-high-reflection fiber grating;

[0034] 400-first cladding gain fiber;

[0035] 500-low-reflection fiber grating;

[0036] 600-first mode stripper;

[0037] 700-end cap;

[0038] 800-mid-infrared isolator;

[0039] 900 - Second pump source, 900a - Third pump source, 900b - Fourth pump source;

[0040] 1000-Pump signal combiner;

[0041] 1100 - Second cladding gain fiber;

[0042] 1200 - Second stripper. Detailed Implementation

[0043] The embodiments of the technical solutions in this specification will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solutions in this specification and should not be construed as limiting the scope of protection of this specification.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this specification belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this specification; the terms “comprising” and “having”, and any variations thereof, in the description of this specification and the foregoing drawings are intended to cover non-exclusive inclusion.

[0045] In the description of the embodiments in this specification, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary or secondary relationship of the indicated technical features. In the description of the embodiments in this specification, "multiple" means two or more, unless otherwise explicitly defined.

[0046] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this specification. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0047] In the description of the embodiments in this specification, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0048] In the description of the embodiments in this specification, the term "multiple" refers to two or more (including two).

[0049] Traditional 2.8 μm band lasers face difficulties in achieving high power, high efficiency, and all-fiber connectivity, making it difficult to simultaneously meet these three objectives, thus necessitating new technological approaches.

[0050] To address this, this application provides a 2.8μm all-fiber laser 10 based on dual-wavelength synergistic cladding pumping. Please refer to [link to relevant documentation]. Figure 1 As shown, the laser includes a first pump source 100, a first cladding gain fiber 400, a mid-infrared pump combiner 200, a high-reflection fiber grating 300, a low-reflection fiber grating 500, a first mode stripper 600, and an end cap 700. The first pump source 100 includes at least one first pump light source 100a and at least one second pump light source 100b. The first pump light source 100a is configured to provide first pump light with a first wavelength, and the second pump light source 100b is configured to provide second pump light with a second wavelength. The first cladding gain fiber 400 is configured to absorb the first and second pump lights and amplify the generated laser to form a 2.8 μm laser. The mid-infrared pump combiner 200 is connected to the first pump source 100 and the first cladding gain fiber 400. Between the first cladding gain fiber 400, the mid-infrared pump combiner 200 is configured to couple the first pump light and the second pump light into the first cladding gain fiber 400; a high-reflectivity fiber grating 300 is connected between the output end of the mid-infrared pump combiner 200 and the input end of the first cladding gain fiber 400; a low-reflectivity fiber grating 500 is connected to the output end of the first cladding gain fiber 400; a first mode stripper 600 is connected to the output end of the low-reflectivity fiber grating 500; and an end cap 700 is connected to the output end of the first mode stripper 600.

[0051] For ease of understanding, the following explains some key terms in this embodiment:

[0052] First pump source 100: refers to the device used to provide energy to excite the gain medium to generate laser light. It usually consists of multiple pump sources, which can generate light of a specific wavelength and transmit the light to the gain medium through optical fiber or free space coupling.

[0053] First-cladding gain fiber 400: This refers to a special type of optical fiber doped with rare-earth ions and other gain media. Pump light is absorbed by the gain media through the fiber's cladding, thus amplifying the signal light. The structure and doping concentration of this fiber are designed to provide gain within a specific wavelength range.

[0054] Mid-infrared pump combiner 200: This refers to an optical device used to combine beams emitted from multiple pump sources and couple the combined pump light into the cladding of a gain fiber. This combiner is typically implemented using fiber fused taper technology or spatial optical elements to ensure efficient transmission and coupling of the pump light.

[0055] High-reflectivity fiber grating 300: This refers to a structure formed by periodically modulating the refractive index inside an optical fiber, which has high reflectivity within a specific wavelength range. In high-power lasers, high-reflectivity fiber grating 300 is typically used as the back-end mirror of the resonant cavity to provide high reflectivity for laser oscillation.

[0056] Low-reflectivity fiber Bragg grating 500: This refers to a structure formed by periodically modulating the refractive index inside an optical fiber, which has low reflectivity within a specific wavelength range. In lasers, low-reflectivity fiber Bragg grating 500 is typically used as the front-end output mirror of the resonant cavity to output a portion of the laser energy.

[0057] First mode stripper 600: refers to an optical device used to remove unwanted modes (such as cladding modes) from an optical fiber. In fiber lasers, mode strippers are typically used to ensure the mode purity of the output laser and to prevent cladding light from affecting the quality of the output laser.

[0058] End cap 700: This refers to an optical element installed at the end of an optical fiber, typically used to prevent damage to the fiber end face and reduce back reflection. In high-power lasers, end cap 700 can effectively reduce the power density of the fiber end face and prevent end face burn-out.

[0059] This embodiment provides a 2.8 μm all-fiber laser 10 based on dual-wavelength synergistic cladding pumping. The laser includes a first pump source 100 configured to provide a first pump light with a first wavelength and a second pump light with a second wavelength. The first pump source 100 may consist of two independent laser diodes, each generating pump light of a different wavelength. Alternatively, the first pump source 100 may consist of an array of multiple laser diodes, with pump light of different wavelengths combined by a beam combiner.

[0060] The first cladding gain fiber 400 is configured to absorb the first and second pump lights and amplify the generated laser to form a 2.8 μm laser. The first cladding gain fiber 400 can be a conventional rare-earth-doped fiber, with its core designed to support laser amplification in the 2.8 μm band. The cladding structure of this fiber is optimized for effective absorption of the pump light.

[0061] A mid-infrared pump combiner 200 is connected between a first pump source 100 and a first cladding gain fiber 400, and is configured to couple the first pump light and the second pump light into the first cladding gain fiber 400. The mid-infrared pump combiner 200 can be a fused taper fiber combiner, which achieves effective coupling of the pump light by fusion splicing multiple pump fibers to a single output fiber.

[0062] A high-reflectivity fiber grating 300 is connected between the output of the mid-infrared pump combiner 200 and the input of the first cladding gain fiber 400. The high-reflectivity fiber grating 300 can be formed by writing inside the fiber using ultraviolet exposure, and its reflectivity is designed to have high reflectivity in the 2.8μm band.

[0063] The low-reflectivity fiber grating 500 is connected to the output end of the first cladding gain fiber 400. The low-reflectivity fiber grating 500 can also be formed by ultraviolet exposure method by writing inside the fiber, and its reflectivity is designed to have low reflection characteristics in the 2.8μm band, so as to serve as the laser output end.

[0064] The first mode stripper 600 is connected to the output of the low-reflection fiber Bragg grating 500. The first mode stripper 600 can be a mechanical mode stripper that removes the cladding mode by using a special coating.

[0065] The end cap 700 is connected to the output end of the first stripper 600. The end cap 700 can be connected to the end of the optical fiber by fusion splicing, and its materials and structure are optimized to withstand high-power laser output.

[0066] With the above structure, the 2.8μm all-fiber laser of this application can effectively utilize the dual-wavelength synergistic pumping mechanism to improve pumping efficiency and laser output power, thereby providing high-power and high-efficiency all-fiber laser output in fields such as medical surgery, environmental monitoring, industrial processing and national defense security.

[0067] In some embodiments of this application, the gain fiber can be pumped by combining two pump lights to improve laser performance. However, in practice, the specific selection of the pump wavelength is crucial for optimizing pump efficiency, effectively managing the thermal load of the gain medium, and achieving stable high-power 2.8μm laser output.

[0068] In some embodiments, the wavelength of the first pump light provided by the first pump source 100 is 976 nm, and the wavelength of the second pump light is 1.7 μm.

[0069] Specifically, the wavelength of the first pump light provided by the first pump source 100a is set to 976 nm. 976 nm is a strong absorption band for rare-earth ions (such as erbium-doped ions), which can efficiently pump ions from the ground state to a high energy level, providing sufficient population inversion for the generation of 2.8 μm laser light. This wavelength pumping technology is mature, and the corresponding semiconductor laser has advantages such as high power, high efficiency, and cost-effectiveness, making it easy to implement.

[0070] Meanwhile, the wavelength of the second pump light provided by the second pump source 100b is set to 1.7 μm. 1.7 μm wavelength pumping is an effective cascade pumping method, capable of exciting rare-earth ions to intermediate energy levels through ground-state absorption. 4 I 13 / 2 Then reach ESA 4 I 9 / 2 Further, through nonradiative transitions to the upper energy level of the laser. 4 I 11 / 2 Compared to 976nm pumping, it has a smaller quantum defect, which helps to significantly reduce the thermal load inside the first cladding gain fiber 400. This is especially important for high-power 2.8μm lasers, as it can effectively suppress performance degradation caused by thermal effects and improve laser stability.

[0071] By combining 976nm and 1.7μm pumping through the above technical solution, a synergistic pumping mechanism is formed. The 976nm pump light provides strong initial excitation, ensuring the rapid establishment and maintenance of population inversion in the first cladding gain fiber 400; while the 1.7μm pump light, with its lower quantum defect characteristics, effectively replenishes energy and reduces heat accumulation in the first cladding gain fiber 400. This dual-wavelength synergistic pumping strategy not only fully utilizes the advantages of the two pump wavelengths and optimizes the absorption and conversion efficiency of pump energy, but also significantly reduces the thermal effects of the first cladding gain fiber 400, thereby enabling the 2.8μm all-fiber laser to achieve higher output power, better beam quality, and longer-term operational stability.

[0072] In the embodiments of this application, a dual-wavelength synergistic cladding pumping method is used to excite the 2.8 μm laser, which may involve combinations of pump lights of different wavelengths, such as a 976 nm pump light and a 1.7 μm pump light. However, when using the 976 nm pump light, due to the large quantum defect between it and the 2.8 μm laser transition, significant heat accumulation occurs inside the gain fiber. This may not only reduce the laser's conversion efficiency but also induce thermal effects, affecting the laser's stability and performance during high-power operation.

[0073] In this embodiment of the application, the all-fiber laser includes a first cladding gain fiber 400, a mid-infrared pump combiner 200, a high-reflection fiber grating 300, a low-reflection fiber grating 500, a first mode stripper 600, and an end cap 700. The first pump source 100 includes at least one first pump light source 100a and at least one second pump light source 100b. The first pump light source 100a is configured to provide first pump light with a first wavelength, and the second pump light source 100b is configured to provide second pump light with a second wavelength. The first cladding gain fiber 400 is configured to absorb the first and second pump lights and amplify the generated laser to form a 2.8 μm laser. The mid-infrared pump combiner 200 is connected between the first pump source 100 and the first cladding gain fiber 400 and is configured to couple the first and second pump lights into the first cladding gain fiber 400. The high-reflectivity fiber grating 300 is connected between the output of the mid-infrared pump combiner 200 and the input of the first cladding gain fiber 400. The low-reflectivity fiber grating 500 is connected to the output of the first cladding gain fiber 400. The first mode stripper 600 is connected to the output of the low-reflectivity fiber grating 500. The end cap 700 is connected to the output of the first mode stripper 600. In this configuration, both the first and second wavelengths are 1.7 μm.

[0074] Specifically, setting the first pump light to 976 nm and the second pump light wavelength to 1.7 μm means that the first pump source 100a provides pump light with a wavelength of 976 nm, and the second pump source 100b provides pump light with a wavelength of 1.7 μm. Compared to a single 976 nm pump light, for example for erbium-doped ions, the 1.7 μm pump light excited-state absorption (ESA) is significantly reduced. 4 I 9 / 2 Energy level, then relax to 4 I 11 / 2 Ultimately achieved 4 I 11 / 2 arrive 4 I 13 / 2 Population inversion of energy levels enables laser transitions at 2.8 μm. This synergistic pumping method significantly improves laser efficiency and reduces the thermal load within the gain fiber.

[0075] By setting the first pump light to 976 nm and the second pump light to 1.7 μm, synergistic pumping of the first cladding gain fiber 400 is achieved. This pumping method significantly improves the laser's output efficiency, thereby greatly increasing the output power of the gain fiber. Furthermore, it achieves a lower thermal load to maintain the temperature stability of the gain fiber, effectively suppressing thermal effects and thus improving the conversion efficiency and output power stability of the 2.8 μm laser.

[0076] Specifically, setting the wavelengths of both the first and second pump lights to 1.7 μm means that both the first pump source 100a and the second pump source 100b provide pump light with a wavelength of 1.7 μm. Compared to 976 nm pump light, for example, please refer to... Figure 3 As shown, for erbium-doped ions, a 1.7 μm pump light can be pumped to the ground state through absorption. 4 I 13 / 2 Energy level, then through excited state absorption (ESA) to 4 I 9 / 2 Energy level, then relax to 4 I 11 / 2 Ultimately achieved 4 I 11 / 2 arrive 4 I 13 / 2 Laser transitions at 2.8 μm energy levels. This cascaded pumping method significantly reduces quantum defect, thereby reducing the thermal load inside the gain fiber.

[0077] By setting the wavelengths of both the first and second pump lights to 1.7 μm using the above technical solution, cascade pumping of the first cladding gain fiber 400 was achieved. This cascade pumping method significantly reduces the quantum defect inside the laser, thereby greatly reducing the heat generated by the gain fiber during operation. The lower thermal load helps maintain the temperature stability of the gain fiber, effectively suppressing thermal effects, thus improving the conversion efficiency and output power stability of the 2.8 μm laser. Furthermore, due to the reduction in thermal effects, the laser's performance at high power operation is optimized, avoiding mode instability or fiber damage caused by overheating, extending the laser's lifespan, and providing favorable conditions for achieving higher power 2.8 μm all-fiber laser output.

[0078] The all-fiber laser provided in this application amplifies the generated laser light through a first cladding gain fiber 400. However, when achieving high-efficiency and high-power 2.8μm laser output, the inherent loss and non-radiative relaxation effects of conventional fiber materials may limit the laser's performance.

[0079] In some embodiments, the first cladding gain fiber 400 is a fluoride-doped cladding gain fiber. Fluoride-doped cladding gain fiber refers to an optical fiber with fluoride glass as the matrix material and rare earth ions (such as erbium, holmium, dysprosium, etc.) as the gain medium. Compared with traditional silicon-based optical fibers, fluoride optical fibers have lower phonon energies, which is crucial for laser emission in the mid-infrared band (e.g., 2.8 μm). In the 2.8 μm band, rare earth ions (e.g., Erbium, holmium, dysprosium, etc.) are highly reactive and doped with fluoride ions. 3+ The energy level transitions of rare-earth ions are easily affected by the phonon energy of the matrix material. The low phonon energy of fluoride glass can effectively suppress the multiphonon relaxation process of rare-earth ions, thereby significantly improving the quantum efficiency and radiation efficiency of 2.8 μm laser transitions and reducing non-radiative losses. Fluoride-clad gain fibers are usually prepared using methods such as MCVD (Modified Chemical Vapor Deposition) or VAD (Vapor-phase Axial Deposition), and rare-earth ions are introduced into the fiber preform. Their structure generally includes a core, inner cladding, and outer cladding, where the core is doped with rare-earth ions, the inner cladding is used for pump light transmission and absorption, and the outer cladding is used for fiber protection and encapsulation. Common fluoride glass matrices include ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) and IGF (InF3-GaF3-ZnF2).

[0080] By employing the aforementioned technical solution, the first cladding gain fiber 400 is configured as a fluoride-doped cladding gain fiber. Utilizing the inherent low phonon energy characteristics of the fluoride glass matrix, the non-radiative relaxation process of rare-earth ions in the 2.8 μm band can be effectively suppressed. This significantly improves the quantum efficiency and radiative efficiency of laser transitions, enabling the laser to convert pump light into 2.8 μm laser output with higher efficiency and achieve higher output power. Simultaneously, the reduced non-radiative loss also helps to lower the internal thermal effects of the fiber, improving the stability and reliability of the laser.

[0081] In the embodiments of this application, the all-fiber laser amplifies the laser beam through a first cladding gain fiber 400. However, in practical applications, to meet the demand for higher power output, a single gain stage may have limited output power. Furthermore, the laser system lacks an effective protection mechanism for the reverse-propagating laser beam, which may affect the system's stability and reliability.

[0082] For this, please refer to Figure 2As shown, the all-fiber laser, based on the above structure, further includes a mid-infrared isolator 800, a second pump source 900, a pump signal combiner 1000, a second cladding gain fiber 1100, and a second mode stripper 1200. The mid-infrared isolator 800 is connected between the first mode stripper 600 and the end cap 700. The second pump source 900 includes at least one third pump source 900a and at least one fourth pump source 900b. The third pump source 900a is configured to provide a third pump light with a third wavelength, and the fourth pump source 900b is configured to provide a fourth pump light with a fourth wavelength. The pump signal combiner 1000 is connected to the mid-infrared isolator 800 and the second pump source 900, respectively, and is configured to couple the 2.8μm laser, the third pump light, and the fourth pump light into the second cladding gain fiber 1100. The second cladding gain fiber 1100 is connected to the output of the pump signal combiner 1000 and is configured to absorb the 2.8μm laser, the third pump light, and the fourth pump light, and amplify the generated laser. The second mode stripper 1200 is connected between the second cladding gain fiber 1100 and the end cap 700.

[0083] Specifically, a mid-infrared isolator 800 is a device that allows light to pass through in one direction while blocking reverse light. Its main function is to prevent reverse-propagating laser light from entering upstream components, thereby protecting the laser source and improving system stability. For the 2.8μm band, mid-infrared isolators 800 are typically designed based on the Faraday effect, using magneto-optical materials that are transparent to this wavelength and have a high Wilderness constant (e.g., doped terbium gallium garnet (TGG) or yttrium iron garnet (YIG) crystals, or specific chalcogenide glasses) and polarizers. It can be implemented in an all-fiber integrated form or in a free-space coupled-fiber configuration.

[0084] The second pump source 900 provides power for the second-stage amplification. This second pump source 900 includes at least one third pump source 900a and at least one fourth pump source 900b. These pump sources can be high-power semiconductor lasers (LDs) or fiber lasers, configured to provide pump light with specific wavelengths. For example, the third and fourth wavelengths can be 976 nm and 1.7 μm, respectively, or both can be 1.7 μm. These sources are output via fiber optic coupling for easy connection to the pump signal combiner 1000.

[0085] The pump signal combiner 1000 is a multi-port fiber optic device used to efficiently couple a 2.8 μm laser signal from a mid-infrared isolator 800, along with third and fourth pump lights from a second pump source 900, into a second cladding gain fiber 1100. This combiner needs to have low insertion loss, high power handling capability, and good combining efficiency for signals of different wavelengths. It typically employs a tapered fiber bundle combiner (TFB) structure, using a fused taper process to combine multiple input fibers into a single output fiber. To ensure compatibility with 2.8 μm lasers, the ports of the pump signal combiner 1000 can be made of fluoride fiber.

[0086] The second-clad gain fiber 1100 is the core component of the second-stage amplification. It is typically a double-clad structure, with the inner cladding used to transmit pump light and the core doped with rare-earth ions (such as erbium ions Er). 3+ This fiber is used to absorb pump light and amplify the 2.8 μm laser. To achieve gain in the 2.8 μm band, the fiber is preferably a fluoride-doped cladding gain fiber, such as erbium-doped fluoride fiber (e.g., Er:ZBLAN fiber), which has low loss and high quantum efficiency in the mid-infrared band.

[0087] The second mode stripper 1200 is connected between the output end and the end cap 700 of the second cladding gain fiber 1100. Its function is to remove cladding mode light generated or not absorbed in the gain fiber, as well as residual pump light, to ensure that the 2.8μm laser output from the fiber core has good mode purity and beam quality. The mode stripper can be implemented by coating the fiber cladding with a high refractive index material or by bending the fiber in a specific way, so that the light in the cladding leaks out while the signal light in the fiber core remains unaffected.

[0088] Through the above technical solution, the introduction of the mid-infrared isolator 800 effectively blocks the reverse-propagating laser, protecting the upstream laser components from damage and significantly improving the system's stability and reliability. Simultaneously, by adding a second pump source 900, a pump signal combiner 1000, and a second cladding gain fiber 1100, a second-stage amplifier is constructed, enabling further power enhancement of the 2.8μm laser. This overcomes the limitation of output power in a single gain stage and meets the application requirements for higher power output. The second mode stripper 1200 ensures the mode purity of the output laser, further optimizing beam quality. Overall, this solution significantly improves the output power and beam quality of the 2.8μm all-fiber laser while ensuring stable system operation.

[0089] In some of the above embodiments, a multi-stage amplification structure is employed to achieve high-power output of the 2.8μm laser. The second cladding gain fiber 1100 amplifies the laser by absorbing the 2.8μm laser, the third pump light, and the fourth pump light. However, in practical applications, if the wavelengths of the third and fourth pump lights are not properly selected, the absorption efficiency of the second cladding gain fiber 1100 for the pump light may be low, thus affecting the energy conversion efficiency, increasing the thermal load, and limiting the final output power and stability of the 2.8μm laser.

[0090] To this end, this application further proposes setting the third wavelength to 976 nm and the fourth wavelength to 1.7 μm. Specifically, the 976 nm wavelength, as the pump light, has a high absorption cross-section in erbium-doped fluoride fiber, enabling efficient injection of pump energy into erbium ions (Er). 3+ In the energy levels of ), for example, directly pumped from the ground state to 4 I 11 / 2 Energy levels. This pumping method effectively establishes population inversion, providing sufficient gain for the generation and amplification of 2.8 μm laser light. Simultaneously, using a 1.7 μm wavelength as the pump light, it can cascade pump erbium ions (Er) to... 3+ Pumping to the energy level 4 I 9 / 2 Then it quickly relaxes to radiation-free levels. 4 I 11 / 2 Energy levels. Compared to 976nm pumping, 1.7μm pumping has a smaller quantum defect, which means less heat is generated during energy conversion. This helps to reduce thermal effects and improve the thermal stability of the laser when operating at high power.

[0091] By setting the wavelength of the third pump light to 976 nm and the wavelength of the fourth pump light to 1.7 μm, this application achieves synergistic pumping of the second cladding gain fiber 1100. Specifically, the 976 nm pump light provides strong energy injection, ensuring sufficient excitation of erbium ions and rapid establishment of population inversion; while the 1.7 μm pump light further optimizes the upper-level particle number with lower quantum defect, effectively reducing heat accumulation inside the gain fiber. This dual-wavelength synergistic pumping strategy fully utilizes the advantages of the two pump wavelengths, namely the high absorption efficiency of 976 nm and the low thermal effect of 1.7 μm, thereby significantly improving the amplification efficiency and stability of the second cladding gain fiber 1100 for 2.8 μm laser. Ultimately, this scheme can effectively improve the output power and beam quality of the entire 2.8 μm all-fiber laser, while extending the laser's lifetime under high-power operation.

[0092] In some embodiments of this application, an all-fiber laser generates and initially amplifies a 2.8 μm laser beam through a first pump source 100 and a first cladding gain fiber 400, and further amplifies the 2.8 μm laser beam through a second pump source 900 and a second cladding gain fiber 1100. However, in the process of achieving secondary amplification, how to select the wavelengths of the third and fourth pump lights provided by the second pump source 900 to ensure that the pump energy can be efficiently absorbed by the second cladding gain fiber 1100 and converted into a 2.8 μm laser beam, while optimizing amplification efficiency and system stability, is a technical problem that needs to be solved. Inappropriate selection of pump wavelengths may lead to low pump light absorption efficiency, failure to effectively establish population inversion, and thus affect the final output power and beam quality of the 2.8 μm laser.

[0093] In some implementations, the third wavelength is 1.7 μm, and the fourth wavelength is 1.7 μm. Specifically, both the third and fourth wavelengths are set to 1.7 μm, meaning that the third and fourth pump lights generated by the second pump source 900 both have a wavelength of 1.7 μm. In 2.8 μm lasers based on erbium-doped fluoride fibers, 1.7 μm wavelength pumping is a highly efficient pumping method. Light of this wavelength can directly and effectively excite ions (e.g., Erbium-doped fluoride fibers) in the gain medium. 3+ (ion), causing it to transition from the ground state to an intermediate energy level. 4 I 13 / 2 Further, through ESA, it jumps to the energy level. 4 I 9 / 2 Then it rapidly relaxes to the upper energy level of the laser. 4 I 11 / 2 This allows for the establishment of population inversion required for the 2.8 μm laser transition. This pumping mechanism significantly reduces quantum defect.

[0094] By setting the wavelengths of the third and fourth pump lights provided by the second pump source 900 to 1.7 μm, this application can provide highly matched and efficient pump energy for the second cladding gain fiber 1100. The 1.7 μm wavelength has good matching with the absorption peak of the gain ions in the fluoride-doped fiber, enabling direct and efficient pumping of the upper energy level, thereby establishing a stronger population inversion in the second cladding gain fiber 1100. This 1.7 μm wavelength pumping method not only provides sufficient pump power, but also significantly improves the amplification efficiency of the second stage because the pump energy can be more effectively absorbed and converted into 2.8 μm laser light, further increasing the output power of the 2.8 μm laser. Simultaneously, it helps reduce waste heat caused by ineffective absorption, thereby improving the thermal stability of the laser.

[0095] In the embodiments of this application, the first cladding gain fiber 400 generates a 2.8 μm laser, which is further amplified by the second cladding gain fiber 1100. However, in the 2.8 μm band, the intrinsic loss of conventional silicon-based fibers is relatively high, which may limit the effective amplification capability and output power of the second cladding gain fiber 1100 for the 2.8 μm laser. Especially in high-power applications, the inherent loss of the fiber material can significantly affect the overall performance and stability of the laser.

[0096] In some embodiments, the second cladding gain fiber 1100 is a fluoride-doped cladding gain fiber. A fluoride-doped cladding gain fiber is a gain fiber with fluoride glass as the substrate material and doped with rare earth ions (such as erbium ions, holmium ions, or dysprosium ions). Compared with traditional silicon-based fibers, fluoride fibers have extremely low intrinsic loss and high transmittance in the mid-infrared band of 2-5 μm, making them an ideal gain medium for 2.8 μm laser amplifiers. As the second cladding gain fiber 1100, its main function is to absorb the third and fourth pump lights and the 2.8 μm laser, and further amplify the 2.8 μm laser. In practical applications, the fabrication process of fluoride fibers requires strict control of material purity and the use of special drawing techniques to ensure its optical performance and mechanical strength. For example, to efficiently amplify 2.8 μm lasers, erbium-doped fibers (Er) are typically selected. 3+ Fluoride optical fibers, because Er 3+ It exhibits a good emission spectrum near 2.8 μm. Simultaneously, the cladding structure design must ensure that the pump light can be effectively coupled and fully absorbed by the gain medium.

[0097] By using fluoride-doped cladding gain fiber 1100 as the second cladding gain fiber, the high intrinsic loss problem of traditional silicon-based fibers in the 2.8μm band is effectively solved. Fluoride-doped cladding gain fiber exhibits extremely low transmission loss and excellent gain characteristics in the mid-infrared band, enabling more efficient absorption and amplification of the 2.8μm laser in the second amplification stage. This not only significantly improves the laser's output power and beam quality but also reduces the internal thermal load of the fiber, thereby enhancing the laser's long-term stability and reliability. Furthermore, the characteristics of fluoride fiber better support the dual-wavelength synergistic cladding pumping mechanism, ensuring that pump energy can be efficiently converted into 2.8μm laser output, further optimizing the overall performance of the all-fiber laser.

[0098] In the embodiments of this application, a 2.8μm laser, a third pump light, and a fourth pump light are coupled into a second cladding gain fiber 1100 via a pump signal combiner 1000 to achieve further amplification of the laser. However, in the 2.8μm band, the absorption loss of conventional silicon-based fiber materials is significant, which may cause the pump signal combiner 1000 to generate high power loss and thermal effects when transmitting optical signals, thereby affecting the output performance and stability of the laser.

[0099] In some implementations, the ports of the pump signal combiner 1000 are all made of fluoride fiber. The pump signal combiner 1000 is a key device for coupling multiple optical signals, and its ports are the interfaces for optical signal entry and exit. Fluoride fiber, such as fiber made from materials like ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) or InF3 (InF3-BaF2-SrF2-GaF3-ZnF2), has extremely low intrinsic absorption loss in the mid-infrared band (especially near 2.8 μm), far lower than that of traditional silicon-based fiber. Using fluoride fiber for all ports of the pump signal combiner 1000 means that all optical signals entering and leaving the combiner, including the 2.8 μm laser, the third pump light, and the fourth pump light, will be transmitted through this low-loss material. This includes not only the signal input port and pump input port, but also the output port after combining. This design ensures efficient transmission of optical signals during coupling, minimizing power loss due to material absorption. The fabrication of fluoride fiber ports typically involves sophisticated fusion splicing or mechanical connection techniques to ensure low-loss connections to the internal structure of the combiner and the external fiber, while maintaining good mechanical strength and environmental stability.

[0100] By employing the aforementioned technical solution, all ports of the pump signal combiner 1000 utilize fluoride fiber, effectively solving the problem of high absorption loss in the 2.8μm band of traditional silicon-based fiber. Due to the extremely low transmission loss of fluoride fiber in the mid-infrared band, the power loss of the 2.8μm laser signal is significantly reduced when passing through the pump signal combiner 1000. Simultaneously, the third and fourth pump lights maintain high transmission efficiency when passing through the fluoride fiber ports. This not only improves coupling efficiency, ensuring more effective optical power can enter the second cladding gain fiber 1100 for amplification, but also enhances the overall laser output power and optical-to-optical conversion efficiency. Furthermore, the reduced optical power loss also significantly reduces heat accumulation inside the pump signal combiner 1000, effectively preventing device performance degradation or damage due to overheating, and enhancing the long-term stability and reliability of the laser system.

[0101] In the embodiments of this application, the laser constructs a basic laser oscillation and amplification structure through components such as a first pump source 100, a first cladding gain fiber 400, and a mid-infrared pump combiner 200, and can further amplify power through components such as a second pump source 900 and a second cladding gain fiber 1100. However, in the process of achieving high-power 2.8μm laser output, a large amount of waste heat is inevitably generated due to the interaction between the pump light and the gain medium and the limitation of quantum efficiency. If this heat cannot be dissipated in a timely and effective manner, it will cause the temperature of the first cladding gain fiber 400, the second cladding gain fiber 1100, and other optical components to rise, thereby triggering thermal effects such as thermal lensing, gain saturation, mode instability, and output wavelength drift. In severe cases, it may even cause irreversible damage to the fiber and devices, thus limiting the output power, stability, and reliability of the laser.

[0102] In some embodiments, the all-fiber laser also includes a water-cooled plate configured to dissipate heat from the all-fiber laser.

[0103] Water-cooled plates are typically made of highly thermally conductive metals, such as copper or aluminum alloys. They have internally designed precision channels for circulating coolant, such as deionized water or specialized coolants. The water-cooled plate conducts heat through close contact with key heat-generating components in the laser, such as the coiled portions of the first cladding gain fiber 400 and the second cladding gain fiber 1100, the pump source module, and the beam combiner. The coolant circulates within the channels, efficiently removing heat from the surfaces of the heat-generating components and dissipating it into the environment through external cooling systems such as radiators and fans. Heat dissipation refers to effectively removing excess heat generated inside the laser to maintain the system operating within a suitable temperature range. For high-power fiber lasers, efficient heat dissipation is crucial for ensuring long-term stable operation. Water-cooled plates utilize the high specific heat capacity and good flowability of the coolant to achieve rapid heat absorption and transfer. By precisely controlling the flow rate and temperature of the coolant, the temperature of the core laser components can be effectively controlled within the design limits, preventing performance degradation or damage due to overheating.

[0104] By introducing and configuring a water-cooled plate to dissipate heat from the all-fiber laser using the above technical solution, the problem of heat accumulation inside the laser under high-power operation can be effectively solved. The water-cooled plate can rapidly dissipate the waste heat generated during pumping and amplification of the first cladding gain fiber 400, the second cladding gain fiber 1100, and other high-heat-generating components, thereby maintaining the temperature of these critical components within a stable operating range. This significantly suppresses thermally induced effects, such as reducing the thermal lensing effect in the gain fiber, which helps maintain good beam quality and mode stability of the laser output. At the same time, the stable temperature environment also avoids output wavelength drift, ensuring the long-term stability and reliability of the laser output power. Therefore, this solution not only improves the overall performance and lifespan of the laser but also provides a solid thermal management foundation for achieving higher-power 2.8μm laser output.

[0105] The following example will provide a more detailed explanation of the above technical solution:

[0106] For precision surgical procedures, a high-power, high-efficiency, and compact 2.8μm all-fiber laser is required. This technical solution provides a 2.8μm all-fiber laser 10 based on dual-wavelength synergistic cladding pumping, which can meet this requirement.

[0107] The laser first comprises an oscillation stage. The first pump source 100 in the oscillation stage consists of multiple first pump sources 100a and multiple second pump sources 100b. The first pump sources 100a provide first pump light with a wavelength of 976 nm, while the second pump sources 100b provide second pump light with a wavelength of 1.7 μm. These two wavelengths of pump light are coupled to a first cladding gain fiber 400 via a mid-infrared pump combiner 200. The first cladding gain fiber 400 is a fluoride-doped cladding gain fiber, which exhibits good absorption characteristics for both 976 nm and 1.7 μm pump light. Compared to a single-wavelength pumping scheme, this dual-wavelength synergistic pumping method can more effectively utilize the absorption spectrum of the fluoride gain fiber, achieving more efficient energy conversion and thus generating 2.8 μm laser light at a lower pump threshold.

[0108] At both ends of the first cladding gain fiber 400, a high-reflectivity fiber grating 300 and a low-reflectivity fiber grating 500 are connected, respectively, forming a resonant cavity. The high-reflectivity fiber grating 300 is connected between the output end of the mid-infrared pump combiner 200 and the input end of the first cladding gain fiber 400, and has high reflectivity for 2.8μm laser light. The low-reflectivity fiber grating 500 is connected to the output end of the first cladding gain fiber 400, and has partial reflectivity for 2.8μm laser light, serving as the laser output end. Under the excitation of the pump light, stimulated emission is generated inside the first cladding gain fiber 400, forming a 2.8μm laser oscillation within the resonant cavity. The 2.8μm laser light generated by the oscillation is output from the low-reflectivity fiber grating 500.

[0109] To ensure the purity of the output laser mode and remove residual pump light and cladding modes, a first mode stripper 600 is connected to the output end of the low-reflection fiber grating 500. This first mode stripper 600 effectively strips light from the cladding, allowing only the 2.8 μm laser light in the fiber core to pass through. Subsequently, an end cap 700 is connected to the output end of the first mode stripper 600 to prevent end-face reflection and protect the fiber end face from damage.

[0110] To further enhance the output power of the 2.8μm laser to meet the demands of high-power surgery, the laser also integrates an amplification stage. The 2.8μm laser output from the oscillation stage first passes through a mid-infrared isolator 800, which prevents the backlight generated by the amplification stage from affecting the oscillation stage, ensuring system stability. The amplification stage includes a second pump source 900, which consists of a third pump source 900a providing a 976nm third pump light and a fourth pump source 900b providing a 1.7μm fourth pump light. A pump signal combiner 1000 couples the 2.8μm laser output from the oscillation stage, the third pump light, and the fourth pump light into a second cladding gain fiber 1100. All ports of the pump signal combiner 1000 use fluoride fiber to ensure low loss in the transmission of the 2.8μm laser. The second cladding gain fiber 1100 is also a fluoride-doped cladding gain fiber, which absorbs the pump light and amplifies the 2.8μm laser. Compared to traditional amplification schemes employing free-space coupling or non-all-fiber structures, this all-fiber amplification stage design significantly improves system integration, stability, and beam quality while reducing losses. The amplified laser passes through a second mode stripper 1200 to remove cladding modes and residual pump light generated during amplification, ultimately outputting a high-power 2.8μm laser.

[0111] During high-power operation, heat is generated inside the laser. To maintain system stability and performance, a water-cooled plate is configured to dissipate heat from the entire all-fiber laser. The water-cooled plate effectively removes heat, preventing overheating that could lead to performance degradation or damage to the laser.

[0112] Through the coordinated operation of the above components, this 2.8μm all-fiber laser based on dual-wavelength synergistic cladding pumping can achieve high-power, high-efficiency 2.8μm laser output. Furthermore, the entire system adopts an all-fiber structure, featuring high integration, high stability, and maintenance-free operation, making it very suitable for applications such as medical surgery that have stringent requirements for laser performance and reliability.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this specification, and not to limit them. Although this specification has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments in this specification.

Claims

1. A 2.8μm all-fiber laser based on dual-wavelength synergistic cladding pumping, characterized in that, include: A first pump source includes at least one first pump light source and at least one second pump light source, wherein the first pump light source is configured to provide first pump light having a first wavelength, and the second pump light source is configured to provide second pump light having a second wavelength; The first double-clad gain fiber is used to absorb the first pump light and the second pump light and amplify the generated laser to form a 2.8μm laser. A mid-infrared pump combiner is connected between the first pump source and the first double-clad gain fiber. The mid-infrared pump combiner is configured to couple the first pump light and the second pump light into the inner cladding of the first double-clad gain fiber to form dual-wavelength cooperative cladding pumping. A high-reflectivity fiber grating is connected between the output end of the mid-infrared pump combiner and the input end of the first double-clad gain fiber, providing high reflectivity for 2.8μm laser light. A low-reflectivity fiber grating is connected to the output end of the first double-clad gain fiber and provides low reflectivity for 2.8μm laser light. The first stripper, connected to the output end of the low-reflection fiber Bragg grating, is used to strip away residual cladding light. The end cap is connected to the output end of the first mold stripper; The first wavelength is 976 nm or 1.7 μm, and the second wavelength is 1.7 μm; Also includes: A mid-infrared isolator is connected between the first stripper and the end cap; The second pump source includes at least one third pump light source and at least one fourth pump light source, the third pump light source being configured to provide third pump light having a third wavelength, and the fourth pump light source being configured to provide fourth pump light having a fourth wavelength. A pump signal combiner is connected to the mid-infrared isolator and the second pump source, respectively. The pump signal combiner is configured to couple the 2.8μm laser, the third pump light and the fourth pump light into the inner cladding of the second double-clad gain fiber to form dual-wavelength synergistic cladding pump. The second double-clad gain fiber is connected to the output end of the pump signal combiner and is configured to absorb the 2.8μm laser, the third pump light and the fourth pump light and amplify the generated laser. The second mode stripper is connected between the second double-clad gain fiber and the end cap; The third wavelength is 976 nm or 1.7 μm, and the fourth wavelength is 1.7 μm; The first double-clad gain fiber is a fluoride-doped clad gain fiber; The second double-clad gain fiber is a fluoride-doped clad gain fiber.

2. The 2.8μm all-fiber laser based on dual-wavelength synergistic cladding pumping according to claim 1, characterized in that, The ports of the pump signal combiner are all made of fluoride optical fiber.

3. The 2.8μm all-fiber laser based on dual-wavelength synergistic cladding pumping according to claim 1, characterized in that, It also includes a water-cooled plate configured to dissipate heat from the all-fiber laser.

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